Magnetic properties of metal-substituted haematite

Mineral and isothermal magnetic properties of Al-, Mn- and Ni-substituted h aematites were characterized and their relationships evaluated in order to interpret better the results of magnetic analyses of soils and recent sedim ents. Aluminium, manganese and nickel haematites generally behaved as singl e-domain (SD) particles. The influence of incorporated Al on the magnetic b ehaviour of haematite was consistent with Al acting as a paramagnetic dilut ent. Mass magnetic susceptibility (chi) and SIRM800 decreased as the level of Al substitution increased. Incorporation of Mn and Ni increased chi, whi ch could be associated with enhancement of the spin canting effect of haema tite. The stability of SIRM800 to demagnetization for Al-haematite appears to be related to a defect mechanism associated with the development of smal ler crystallites arising from Al substitution. Magnetic domain rotation or flipping was probably inhibited, being blocked by structural defects during magnetization and demagnetization, and resulted in a low but stable partia l SIRM (SIRM800). %IRM/SIRM800 demagnetization curves and estimated (B-o)(C R) values of less than or equal to 100 mT for Mn-haematite indicate pseudos ingle-domain/multidomain-like behaviour despite Mn-haematite having particl e and crystallite dimensions similar to Ni-haematite, which did not show th is behaviour. Data indicate that parameters involving unsaturated, partial SIRM should be used with caution in magnetic studies of soils and sediments .